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Abstract:

A battery pack with phase change materials (PCM). The PCM would improve
the heating and cooling capabilities under various vehicle operating
conditions. Methods of controlling the temperature in battery packs are
also described.

Claims:

1. A battery pack comprising: a battery cell; and a compressible isolator
sheet containing a phase change material next to the battery cell.

2. The battery pack of claim 1 wherein the phase change material has a
phase change from liquid to solid at a temperature of less than about 0
C.

3. The battery pack of claim 1 wherein the phase change material has a
phase change from solid to liquid at a temperature of greater than about
40 C.

5. The battery pack of claim 4 wherein the first phase change material
has a phase change from liquid to solid at a temperature of less than
about 0 C and the second phase change material has a phase change from
solid to liquid at a temperature of greater than about 40 C.

6. The battery pack of claim 1 further comprising a cooling fin next to
the battery cell.

7. The battery pack of claim 6 wherein the compressible isolator sheet
and the cooling fin are on opposite sides of the battery cell.

8. The battery pack of claim 6 wherein the cooling fin is cooled by a
liquid and wherein the liquid contains an additional phase change
material.

9. The battery pack of claim 8 wherein the additional phase change
material has a phase change from solid to liquid at a temperature of
greater than about 100 C.

10. The battery pack of claim 6 wherein the cooling fin includes a layer
of foam containing a second phase change material.

11. The battery pack of claim 1 wherein the compressible isolator sheet
is made of a compressible foam.

12. The battery pack of claim 1 further comprising a battery disconnect
unit or a battery management system or both and a pad containing a phase
change material in contact with the battery disconnect unit or the
battery management system or both.

13. A method of controlling temperature in a battery pack comprising:
providing a battery cell; providing a compressible isolator sheet
containing a phase change material next to the battery cell.

14. The method of claim 13 wherein the phase change material has a phase
change from liquid to solid at a temperature of less than about 0 C.

15. The method of claim 13 wherein the phase change material has a phase
change from solid to liquid at a temperature of greater than about 40 C.

17. The method of claim 13 further comprising a cooling fin next to the
battery cell.

18. The method of claim 17 wherein the cooling fin is cooled by a liquid
and wherein the liquid contains an additional phase change material.

19. The method of claim 18 wherein the additional phase change material
has a phase change from solid to liquid at a temperature of greater than
about 100 C.

20. The method of claim 17 wherein the cooling fin further comprises a
layer of foam containing a phase change material.

21. The method of claim 13 wherein the compressible isolator sheet is
made of a compressible foam.

22. The method of claim 13 further comprising a battery disconnect unit
or a battery management system or both and a pad containing a phase
change material in contact with the battery disconnect unit or the
battery management system or both.

23. A battery pack comprising: a battery cell; a battery disconnect unit
or a battery management system or both; and a pad containing a phase
change material in contact with the battery disconnect unit or the
battery management system or both.

Description:

[0002] This invention relates generally to battery packs and more
particularly to battery packs using phase change materials, and to
methods of controlling the temperature in a battery pack using a phase
change material.

[0003] Most passenger vehicles are parked about 90% of the time. In
general, both energy (discharge capacity) and power (operating voltage)
of Li-ion batteries are substantially reduced as the temperature falls
below about -10 C. At higher temperature (greater than about 45 C),
battery life is substantially degraded. Current liquid-based vehicular
Li-ion battery cooling systems lack the capability of rapid heat
dissipation during battery thermal runaway.

BRIEF DESCRIPTION OF THE DRAWING

[0004] The FIGURE shows one embodiment of a portion of a battery pack.

DETAILED DESCRIPTION

[0005] A battery, for example a lithium ion battery, with phase change
materials (PCM) would improve the heating and cooling capabilities under
various vehicle operating conditions. The PCM could help to minimize
unnecessary operating temperature swings, increase heating and cooling
uniformity, and reduce heating and cooling requirements.

[0006] Batteries utilizing PCM can control the temperature excursions and
maintain temperature uniformity without, or with reduced use of, active
cooling components such as fans, blowers, or pumps found in
air/liquid-cooling systems. As a result, a compact, light-weight, and
energy efficient system can be achieved, and the energy usage with
battery life and performance throughout the operating range of the hybrid
electric vehicle (HEV)/plug-in electric vehicle (PEV) can be optimized.

[0007] The thermal properties of various PCM and methods of heat transfer
enhancement are described in Kenisarin and Mahkamov, "Solar energy
storage using phase change materials," Renewable and Sustainable Energy
Reviews 11 (2007) 1913-1965, which is incorporated herein by reference.
Tables 1-3 show properties of some commercially available PCM.

[0008] The FIGURE shows one embodiment of a portion of a battery pack 10.
The battery pack 10 has an end frame 15 and repeating frame 20. The end
frame 15 can have an edge portion 25 surrounding a cooling plate 30. The
cooling plate 30 for the end frame can have ribs for added stability, if
desired. There are battery cells 35, cooling fins 40, and compressible
isolator sheets 45. The battery pack 10 will typically include one or
more battery cells 35, one or more compressible isolator sheets 45, one
or more cooling fins 40, and one or more repeating frames 15. The
compressible isolator sheets 45 and cooling fins 40 are next to the
battery cells 35. The compressible isolator sheets 45 and cooling fins 40
are desirably on opposite sides of the battery cell 35, although this is
not required. The compressible isolator sheets 45 are typically in
contact with the battery cell 35, but they do not have to be. For
example, if a very large amount of cooling is needed, there could be a
cooling fin 40 on both sides of the battery cell 35, and the compressible
isolator sheet 45 could be in contact with the cooling fins 40. Various
arrangements of battery pack 10 components could be used, as is known to
those of skill in the art.

[0009] The compressible isolator sheet 45 absorbs the cell expansion
during cycling so that the cell can maintain a desired cell compression.
The material should have long-term compressive strength and thermal
performance. Suitable materials include, but are not limited to,
compressible foam materials. Suitable compressible foam materials
include, but are not limited to, polystyrene foam. One example of a
suitable foam is Styrofoam® brand Highload® 100 insulation (e.g.,
Type V), which has a minimum compressive strength of 100 psi (690 kPa)
available from The Dow Chemical Co.

[0010] There is at least one phase change material (PCM), and desirably,
at least two different PCM, in the compressible isolator sheet 45 of the
battery pack to form a thermal composite. The PCM are materials that
change phase at certain temperatures and are capable of storing and
releasing large amounts of energy. Heat is absorbed or released when the
materials change phase, from solid to liquid, or liquid to solid, for
example. For example, one PCM could change its phase at a low temperature
limit, such as about freezing or below (e.g., less than about 0 C, or
less than about -5 C, or less than about -10 C, or about -10 C, or in a
range of about 0 C to about -10 C), and another at a high temperature
limit (e.g., above about 40 C, or above about 45 C). Thermal insulation
of battery cells using PCM can maintain battery cell temperature for
longer periods of time under extreme temperature conditions. Additional
PCM with different phase change temperatures could also be included, if
desired.

[0011] Desirably, the PCMs have phase change temperatures near the desired
temperatures and large heat capacity values. Although these are suggested
temperatures (ranges), other temperatures (ranges) could be selected, if
desired, as is known to those of skill in the art. A large number of PCMs
are available in any desired temperature range from about -10 C to about
190 C.

[0012] The use of PCM will provide the ability to maintain the cell
temperature in a desired temperature range without drawing power from the
battery or another energy source. It will also improve cell
cycle/calendar life under extreme parking conditions.

[0013] PCMs in close contact with the battery cells can result in one or
more of: reduced power fade, reduced capacity fade, improved battery life
and durability, reduced warranty costs, improved vehicle range, and
preventing or reducing thermal runaway.

[0014] The end frames 15 and the repeating frames 20 for the battery pack
10 are typically made of a light-weight, non-conductive material.
Suitable materials include, but are not limited to, plastics, such as
polypropylene, nylon 6-6, and other low cost materials. The frames 15 can
be fiber-reinforced for structural strength, if desired.

[0015] The cooling fins 40 can be single plates or multilayer structures,
depending on the cooling needs of the particular application. The cooling
fins 40 can be made of any conventional cooling material. Suitable
materials include, but are not limited to, light-weight thermal
conductors such as aluminum, alumina, copper, aluminum silicon carbide,
beryllium oxide, and the like, or sandwich structures of two light-weight
thermal conductors separated by a layer of compressible foam or other
expansion compensator to allow for expansion and contraction of the
battery cells 35 on either side of the cooling fin 40 caused by the
charge state, heating, and cooling of the cells. It can incorporate
integrated heat pipe technology, if desired. There can be a film for
electrical isolation on the cooling fin 40, if desired. In addition,
there could be a foam sheet with PCM on the cooling fins 40. The PCM in
the foam sheet on the cooling fin 40 would likely have the same phase
change temperature as the PCM in the compressible isolator sheet 45,
although this is not necessary.

[0016] The cooling fins 40 can be air or liquid cooled/heated. For air
cooling/heating, the cooling fin can be as simple as a flat metal sheet.
For liquid cooling/heating, the fins have coolant channels in between two
welded metal plates as well as coolant inlets and coolant outlets. The
coolant inlets and outlets can be individually connected to a manifold
for coolant circulation, or they can extend from the fins in ear-shaped
features 50, as described in U.S. patent application Ser. No. 12/774,873,
filed May 6, 2010, entitled Easy-To-Assemble Battery Pack With Prismatic
Battery Cells; and U.S. patent application Ser. No. 12/853,620, filed
Aug. 10, 2010, entitled Integrated Cooling Fin And Frame which are
incorporated herein by reference. To fill up the gap between the cooling
fins 40 and to provide proper coolant sealing, the ear-like extensions 50
can be molded with plastic that is sealable or having rubber seals around
the openings for coolant. The coolant can thus be easily fed into and
removed from end plates of the stack. Fluid manifolds are attached to the
fluid inlets and outlets to distribute the cooling fluid through the
cooling channels. The manifolds can be brazed onto the fluid inlets and
outlets, if desired. Alternatively, the manifolds can be connected using
removable connection, such as with seals. The use of removable
connections improves serviceability.

[0017] PCM can be included in the liquid coolant with a phase change
temperature at a higher temperature (e.g., greater than about 100 C, or
greater than about 150 C, or about 100 C to about 200 C, or about 150 C
to about 200 C). The liquid coolant with PCM additives which melt and
solidify at certain temperatures which are capable of storing and
releasing large amounts of energy can prevent catastrophic battery
failure.

[0018] In another embodiment, because of higher stiffness, the cooling
fins 40 can be the primary structural and locating members of the stack
to hold battery cells (rather than using the repeating frames), as
described in U.S. patent application Ser. No. 12/774,873. In this
arrangement, after compression, the stack can be contained in removable
restraints, including, but not limited to, clamping with bolts or tie
rods, wrapping with metal straps, or boxing in a hard case, for the final
assembly, which saves the weight and cost of repeating frames, as well as
assembly time. In remanufacturing, the stack can be easily disassembled
because of the weld-free assembly, and any bad cells or other components
can be replaced with minimal time and cost.

[0019] Additionally, PCM could be included for various power electronics
components for the battery pack 10, including, but not limited to, the
battery disconnect unit (BDU), the battery management system (BMS), and
the like. Currently, those components are not cooled in liquid cooled
battery packs. However, they are located very close to the battery cell
modules, which could heat up nearby cells. As a result, it could create
non-uniform degradation of the cells and cause an imbalance between them.
A pad containing PCM could be placed under the BDU or BMS control
hardware.

[0020] One important advantage of the present invention is the ability to
cool a battery pack when a vehicle containing the battery pack 10 is
parked at high temperature for an extended period (e.g., in an uncovered,
long term parking facility in Arizona in the summer). Another advantage
is reducing or eliminating of the need for a liquid or air cooling system
inside the battery pack. Elimination of the cooling system would allow
the removal of components such as the coolant reservoir, coolant pump,
and coolant hoses for a liquid cooled system, or fans and air ducts for
an air cooled system.

[0022] It is noted that terms like "preferably," "commonly," and
"typically" are not utilized herein to limit the scope of the claimed
invention or to imply that certain features are critical, essential, or
even important to the structure or function of the claimed invention.
Rather, these terms are merely intended to highlight alternative or
additional features that may or may not be utilized in a particular
embodiment of the present invention.

[0023] For the purposes of describing and defining the present invention
it is noted that the term "device" is utilized herein to represent a
combination of components and individual components, regardless of
whether the components are combined with other components. For example, a
"device" according to the present invention may comprise an
electrochemical conversion assembly or fuel cell, a vehicle incorporating
an electrochemical conversion assembly according to the present
invention, etc.

[0024] For the purposes of describing and defining the present invention
it is noted that the term "substantially" is utilized herein to represent
the inherent degree of uncertainty that may be attributed to any
quantitative comparison, value, measurement, or other representation. The
term "substantially" is also utilized herein to represent the degree by
which a quantitative representation may vary from a stated reference
without resulting in a change in the basic function of the subject matter
at issue.

[0025] Having described the invention in detail and by reference to
specific embodiments thereof, it will be apparent that modifications and
variations are possible without departing from the scope of the invention
defined in the appended claims. More specifically, although some aspects
of the present invention are identified herein as preferred or
particularly advantageous, it is contemplated that the present invention
is not necessarily limited to these preferred aspects of the invention.